Energy Flow in Ecosystems Science 10

Trophic Levels  Trophic levels refer to feeding levels in an ecosystem. They help to explain food and energy distribution in an ecosystem.  1st trophic level = producers  2nd trophic level = primary consumers  3rd trophic level = secondary consumers  4 th trophic level = tertiary consumers

4 th TL Consumer s 3 rd Trophic Level Carnivores 2 nd Trophic Level Herbivores 1 st Trophic Level Producers

Detritivores and Decomposers  Detritivores – organisms that consumes dead material and animal wastes; including decomposers  Decomposers – various bacteria and fungi that break down dead material and animal wastes and extract the remaining nutrients

 Trophic levels show the transfer of energy through a food chain.  On average, only 10% of energy from one trophic level is transferred to the next level. Why?

Energy Use by an Organism  All living organisms use energy to move, grow, reproduce and carry out activities.  As a result:  30% of energy gets converted to thermal energy through cellular respiration  60% of energy gets converted into waste  Only 10% of energy is converted into body tissue, usable at the next level.

 There are various tools to explain the relationship between each trophic level including the three pyramids found on pages 14, 16 and 17.

Benefits  It shows how MANY organisms are at each level so we can estimate the energy available.  It helps explain why there are fewer organisms higher up the food chain Drawbacks  Sometimes, small herbivores and carnivores outnumber the organism they consume so the pyramid does not reflect the energy flow.  Think of the number of insects that can feed on a tree. Pyramid of Numbers page 14

Biomass: the total dry mass of a given population of organisms.

Pyramid of Biomass page 16 Benefits  Shows how MUCH of a living organism is at each level so we can estimate how much energy is available.  Biomass can be several small organisms at a trophic level, or a few big organisms at a trophic level. Drawbacks  Sometimes, producers reproduce very quickly, but the total biomass is lower than the primary consumers, making the pyramid upside down.  Example: zooplankton and algae

Pyramid of Energy page 17 Benefits  A pyramid of energy demonstrates the flow of chemical energy through each trophic level.  It cannot be inverted because there is always less energy available as you go up a trophic level. Drawbacks  Energy pyramids do not reflect the quantity of organisms.